# Monomers, polymers and macromolecules

The topic of "Monomers, Polymers, and Macromolecules" describes the fundamental organizational principle of many biological molecules essential for life.

* **Monomers**: These are the **small, basic molecular units** from which larger molecules are constructed. Examples of monomers include:
  * **Monosaccharides**, such as glucose, galactose, and fructose, are the monomers for carbohydrates.
  * **Amino acids** are the monomers for proteins. There are 20 common amino acids that differ only in their side (R) group.
  * **Nucleotides** are the monomers that make up DNA and RNA. A nucleotide is composed of a pentose sugar, a nitrogen-containing organic base, and a phosphate group.
  * While not polymers themselves, **fatty acids and glycerol** are the building blocks for lipids like triglycerides.
* **Polymers**: These are **large, complex molecules formed when a large number of monomers are joined together**. Most carbohydrates, proteins, and nucleic acids are polymers.
* **Macromolecules**: This term refers to **giant molecules**. Many biological polymers are macromolecules. For instance, polysaccharides and proteins are described as macromolecules. Lipids, however, are generally not considered macromolecules, as they are relatively smaller, though they may clump together.
* **Formation and Breakdown of Polymers**:
  * **Condensation Reactions**: Most biological polymers are formed from their monomers through **condensation reactions**. This process involves **joining two molecules together with the formation of a chemical bond and the elimination of a molecule of water**.
  * **Hydrolysis Reactions**: Biological polymers can be broken down into monomers by **hydrolysis reactions**. This reaction **breaks a chemical bond between two molecules and involves a molecule of water**, making it essentially the opposite of a condensation reaction.
* **Diversity and Commonality**: The variety of life, both past and present, is extensive, but the biochemical basis of life is similar for all living things. This similarity suggests a common ancestor for animals and plants. The close relationship between the structure of molecules and their functions is a striking principle in molecular biology.